1. Field of the Invention
The present invention relates to an angular velocity sensor applicable to various systems for a moving subject, such as an aircraft or vehicle, for example, attitude control systems and navigation systems.
2. Description of the Background Art
Heretofore, this type of angular velocity sensor has been designed in a structure as shown in FIG. 12, which is disclosed, for example, in Japanese Unexamined Patent Publication No. 10-332378.
FIG. 12 is a perspective view of a vibration element provided in a conventional angular velocity sensor. FIG. 13 is a circuit diagram of this angular velocity sensor, and FIG. 14 is a perspective view of the vibration element installed in a case of the angular velocity sensor.
As shown in FIGS. 12 to 14, vibration element 1 has a rectangular parallelepiped shape, and comprises a first piezoelectric substrate 2, and a second piezoelectric substrate 4 attached to first piezoelectric substrate 2 through an electrode layer 3. Further, two segmented electrodes 5 having both functions of driving and detection are attached on a top surface of the vibration element 1, and a common electrode 6 is attached on a bottom surface of the vibration element 1.
Reference numeral 7 indicates four terminals having an approximately Z shape. Each of the terminals 7 has one end formed as a broadened portion 8. This broadened portion 8 is soldered onto a corresponding one of the segmented electrodes 5 of the vibration element 1 to allow one end of the terminal 7 to be fixedly supported by the segmented electrode 5. Another end of the terminal 7 protrudes outward. The broadened portion 8 of the terminal 7 is positioned at a vibrational node in the vibration element 1.
The conventional angular velocity sensor has a circuit configuration as shown in FIG. 13. Specifically, an oscillator circuit 9 serving as driving means has one output terminal connected to respective segmented electrodes 5 through parallel lines each having a resistor 10 interposed therein, and another output terminal connected to the common electrode 6. One of the segmented electrodes 5 is connected to a non-inverting input terminal (+) of a differential amplifier circuit 12 through a resistor 11, and another segmented electrode 5 is connected to an inverting input terminal (−) of the differential amplifier circuit 12 through a resistor 11. Further, a resistor 13 is interposed in a line connecting between an output terminal of the differential amplifier circuit 12 and the inverting input terminal (−) of the differential amplifier circuit 12. As shown in FIG. 14, the vibration element 1 and the terminals 7 are disposed inside of case 14.
An operation of the above conventional angular velocity sensor will be described below.
In response to applying a driving signal, such as a sinusoidal signal generated from the oscillator circuit 9, to the segmented electrodes 5 through the resistors 10, each of the first piezoelectric substrate 2 and the second piezoelectric substrate 4 bendingly vibrates in a direction orthogonal to a principal plane thereof. Then, when the vibration element 1 is rotated around its axis, a Coriolis force will be generated in proportion to an angular velocity of this rotation. This generated Coriolis force acts in a direction parallel to the principal plane of the first and second piezoelectric substrates 2, 4 and orthogonal to the axis of the vibration element 1. The Coriolis force causes a change in direction of a bending vibration of the vibration element 1, and each of the segmented electrodes 5 generates a signal proportional to the angular velocity. Then, the differential amplifier circuit 12 receives the signal generated in each of the segmented electrodes 5 through the corresponding resistor 11 to detect an angular velocity acting on the angular velocity sensor.
From a viewpoint of improving durability of the angular velocity sensor, it is conceivable to enclose the case 14 in an additional receiving member (not shown) to form a case having a double-walled structure so as to provide enhanced durability of the angular velocity sensor.
However, this structure involves difficulties in inspecting or managing an amount of solder for soldering the receiving member to the case 14 during an operation for surface-mounting the case 14 onto the receiving member. This problem becomes serious along with progress in downsizing of the angular velocity sensor. An insufficient amount of solder during soldering causes a problem in that an unstable or unreliable electrical connection between the case 14 and the receiving member is realized, and deterioration in accuracy of an output signal of the angular velocity sensor is also realized.